Turned a straight and got scared

[NIX]

First hand at table, so no reads. When I selected it from the lobby, it had ~60% to the flop and an average pot around 6BB if that adds anything.

Also, MP has 3BB left in his stack after he 3-jacks the turn. May be borderline stacking off.

Full Tilt 0.50/1 Hold'em (6 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: 2+2 Forums)

Preflop: Hero is BB with 6[img]/images/graemlins/spade.gif[/img], 9[img]/images/graemlins/diamond.gif[/img].
UTG calls, MP calls, CO calls, <font color="#666666">2 folds</font>, Hero checks.

Flop: (4.50 SB) 7[img]/images/graemlins/diamond.gif[/img], 5[img]/images/graemlins/diamond.gif[/img], J[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(4 players)</font>
Hero checks, UTG checks, MP checks, CO checks.

Turn: (2.25 BB) 8[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(4 players)</font>
<font color="#CC3333">Hero bets</font>, <font color="#CC3333">UTG raises</font>, <font color="#CC3333">MP 3-bets</font>, CO calls, Hero ???

I don't have the nut straight and I think a chop is unlikely. However T9 wouldn't be unreasonable as well as a flush. Are we folding here, or trying to get to showdown cheaply, or even something else, if the river isn't a diamond?